1. Field of the Invention
The invention relates to a process for preparing low-chloride or chloride-free functional organosilanes by reacting chlorofunctional organosilanes with organic amines or ammonia and separating off the organic hydrochlorides or ammonium chloride thus formed, and also to aminofunctional organosilanes prepared according to the invention.
2. Discussion of the Background
Aminofunctional organosilanes are used conventionally in foundry technology as processing aids. They are also used as coupling agents for storage-stable resins or for glass fibre sizes.
Aminofunctional organosilanes are predominantly prepared by reaction of chlorofunctional organosilanes with organic amines of a wide variety of types or with ammonia. Aminofunctional organosilanes thus formed depend on the selected stoichiometric ratio of the amine component or the ammonia to the chlorofunctional organosilane. In the preparation of an aminofunctional organosilane compound, the procedure is generally to use at least 2 mol of amine or ammonia per mole of chloro-functional organosilane, so that, besides the formation of the aminofunctional organosilane, there is still sufficient amine component available to convert the chlorine replaced into the corresponding amine hydrochloride or ammonium chloride.
Various methods are used for separating off the amine hydrochloride or ammonium chloride formed in the synthesis from the target product, the aminofunctional organosilane.
For example, in the reaction of ammonia with 3-chloropropyltriethoxysilane, the amounts of ammonium chloride not dissolved in the aminopropyltriethoxysilane formed can be separated off from the product by simple filtration. Unfortunately, the remaining ammonium chloride dissolved in the aminopropyltriethoxysilane are disadvantageous for many applications. The ammonium chloride content of the product can be significantly lowered if the crude reaction product prior to filtration has added to it appropriate amounts of an inert medium, e.g. hydrocarbons such as petroleum ether, hexane or xylene, in which the aminosilane but not the ammonium chloride is soluble. Despite these measures, a residual amount of ammonium chloride remains in the filtrate. The usability of these aminosilane thus remains limited.
in other cases, in the preparation of aminofunctional, especially multiply aminofunctional, organosilanes, liquid two-phase systems are formed after the reaction is complete. Thus, for example, in the reaction of chloroorganofunctional silanes with ethylenediamine, the upper phase contains the product contaminated with excess amine and the dissolved hydrochloride thereof. After distillative removal of the amine component used, amine hydrochloride-containing doubly amino-functional organosilane remains which cannot be used in that form present, since its chloride content has an unfavorable influence on the properties of the product.
Reactions of chlorofunctional organosilanes with triply aminofunctional anilines frequently result neither in partial precipitation of the amine hydrochlorides formed in solid form nor in formation of phase systems. The removal of the amine hydrochlorides dissolved in the reaction system formed can be carried out only by appropriate dilution of the reaction product/amine hydrochloride/amine system with inert media in which the amine hydrochloride is not soluble. Even then, undesired residual amounts of amine hydrochloride remain in the product obtained after distillative removal of the inert medium and the amine component used in excess.
Despite the measures used in the preparation of amino-functional organosilanes to separate off the organic hydrochlorides or the ammonium chloride formed, the products still contain undesired amounts of chlorides which limit the use opportunities of the products thus obtained or impair the desired effects.